The present invention relates generally to implantable medical leads and more particularly to implantable cardioversion and defibrillation leads.
Implantable cardioversion/defibrillation leads are employed to deliver electric shocks to the heart to convert tachycardias and fibrillation to normal sinus rhythm. In conjunction with this function, it is desirable that the electrodes are configured and located appropriately relative to the patient's heart to accomplish cardioversion and defibrillation at the lowest possible energy levels. In order to achieve this result, quite a number of electrode configurations and locations have been proposed. For example, multiple electrode configurations are disclosed in U.S. Pat. No. 5,174,288 issued to Bardy, U.S. Pat. No. 4,817,608 issued to Shapland et al., U.S. Pat. No. 4,662,377 issued to Heilman et al. and U.S. Pat. No. 5,111,811 issued to Smits. As a practical matter, no one electrode configuration is optimal for all patients. In addition, patients' hearts may differ substantially in size and in disease states. As such, there has been interest in providing cardioversion/defibrillation leads which have some form of adjustment available to vary either the location of or the size of the cardioversion/defibrillation surface. Sliding sleeves, for example, have been employed in conjunction with the leads described in U.S. Pat. No. 4,735,205 issued to Chachques et al., U.S. Pat. No. 5,578,067 issued to Ekwall et al., U.S. Pat. No. 5,383,922 issued to Zipes et al. and pending U.S. patent application Ser. No. 08/821,899 filed on Mar. 21, 1997 by Michael Hill, for adjustment of position and/or length of cardioversion/defibrillation or other electrode surfaces.
An additional alternative approach to physically reconfiguring the location or length of the cardioversion/defibrillation electrode is to accomplish the same result electrically by selecting between different electrodes located along the length of the lead to effectively provide cardioversion/defibrillation electrodes optimized with respect to location and/or length, as disclosed in U.S. Pat. No. 5,174,288 issued to Pohndorf et al.